Aluminum-calcium alloys



Patented July 20, 1937 ALUMINUM-CALCIUM ALLOYS Philip '1.- Stroup, NewKensington, Pa; assignor to Aluminum Company of America, Pittsburgh,Pa., a corporation of Pennsylvania No Drawing. Application April 29,1936, Serial No. 77,020

4 Claims.

I This invention relates to aluminum base alloys containing calcium andit is more particularly concerned with a means of producing soundcastings. I

Aluminum base alloys consisting of aluminum and 2 to 15 per cent calciumfind commercial use both as material from which certain articles aremade and as a source of calcium in the manufacture of other alloys. 4 IIn making aluminum base alloys containing calcium it is preferable toadd this element as a constituent in a rich alloy rather than inelemental form to avoid undue loss and excessive oxidation. Hence it isthe customary practice to employ a calcium-bearing alloy of the kindmentioned above. 1

The manufacture of the aluminum-calcium alloys themselves involves somedifficulty by reason of the readiness with'which they oxidize in themolten condition and their marked tendency to sorb gas from theatmosphere. The oxide particles formed on the surface of the metalappear to hold onto considerable gas when they become mingled with themolten metal and thus in eifect become a source of gas when conditionschange and the particles are no longer able to retain their gas charges.This phenomenon of gas release is manifested during the solidificationof the alloy. During this process the affinity between the metal, theoxide particles and the sorbed gas is greatly reduced and the gas formsbubbles in the liquid metal. If the metal is in a sufilciently fluidstate the bubbles may escape, otherwise they are trapped and formspacesin the casting. Furthermore, in the case of the rich alloys, the voidspaces contain gas which is released in the melt to which the alloys arei added. The deleterious effect of gas isthus transferred to otheralloys.

o Aluminum-calcium alloys also exhibit another disadvantageous featurewhen solidifying, namely, the formation of excrescences on the head orupper surface of the castings which necessitates discarding this portionof the casting.

45 My invention is accordingly directed to a means of eliminating orgreatly reducing the formation i of the void spaces in aluminum-calciumalloys,

65 spaces in the solidifying alloy and does away with the protuberancesnormally occurring on the top surface of the frozen alloy. '1 havefound, for example, that the addition of 0.05 per cent sodium to analloy composed of aluminum and 14 per cent calcium completely removesthe objection- 5 able porosity ordinarily occurring in such an alloy. Ihave also found that such a sodium treated alloy does not introduce gasinto other aluminum base alloys to which it may be added, thus carryingover the benefit of sodium into the 10 final product. t

In order to be effective the sodium should be added shortly'before thealuminum-calcium alloy is poured into the mold. In this manner themaximum amount of sodium is retained in the 1 alloy. This element mustremain in the alloy, especially where the latter is to be added toanother melt. I am aware that sodium has been heretofore employed inmodifying the structure of aluminum alloys containing substantial 20amounts of silicon, and in certain treatments when it iscompletelyremoved from the alloy after it has been added. My invention, however,is clearly distinguishable from such prior uses of sodium inthat Iemploy it to suppress the 25 'action of the calcium, and it is necessaryto retain the sodium in the alloy to accomplish this purpose.

In referring to the proportions of sodium to be added to the moltenalloy, allowance must be 30 made for the escape of a certain portion ofthe element because .of its volatility at the temperature of moltenaluminum and its great tendency to burn. It is therefore usuallynecessary to add more sodium than is ultimately desired in the 5 alloyto compensateior any losses. In stipulating that 0.005 to 0.1 per centsodium should be added to the herein described aluminum-calcium alloys,I mean that at least this amount of sodium should'remain in the finalproduct. The 40 sodium is in fact a positive constituent of the alloy.If smaller amounts of this element than 0.005 per cent are employed, thebenefit in respect to reducing porosity is negligible. On the" otherhand, amounts larger than about 0.1 per cent do not show anycommensurate effect upon the gas content of the alloy. For mostpurposes, however, I prefer to use no more than 0.05 per cent sodiumbecause of the difliculty of adding I and retaining a larger amount ofthe element in the alloy. 7

The sodium should be added to the molten aluminum-calcium alloy in theelemental form. This is preferably done by wrapping pieces of the metalin aluminum foil, placing them in a persilicon, and the like.

suppress the action of calcium in promoting the formation of oxideparticles and the sorption of gas. My invention is applicable totreating such alloys also since it pertains primarily to inhibiting theaction of calcium. These alloys as well as the binary aluminum-calciumalloys are characterized by a relative freedom from gas, and theresultant porosity of the casting when 0.005 to 0.1 per cent sodium ispresent.

The term aluminum as herein employed refers to the metal containing theusual impurities of iron, silicon and the like. The calcium also maycontain impurities usually associated with this metal.

I claim: 7

1. An aluminum base alloy containing. from 2 to 15 per cent calcium and0.005 to 0.1 per cent sodium, said alloy being characterized bysubstantial freedom from porosity attributable to the presence of gas inthe metal.

2. An aluminum base alloy composed of from 2 to 15 per cent calcium,0.005 to 0.1 per cent sodium, and the balance aluminum.

3. An aluminum base alloy composed of from 2 to 15 per cent calcium,0.005 to 0.05 per cent sodium, and the balance aluminum.

4. An aluminum base alloy composed of 14 per cent calcium, 0.05 per centsodium, and the balance aluminum.

PHILIP T. STROUP.

